The Flow Cytometry Core has been in continuous operation under the direction of Dr. Robert Todd (10% effort) since October 1984. The Core provides flow cytometry instrumentation and expertise to members of the University of Michigan Multipurpose Arthritis Center (UM-MAC), A center scheduled for phase-out in 2001. We propose to continue this core as an essential resource for the UM-Rheumatic Disease Core Center (UM-RDCC). Current UM-MAC investigators, with additions, will continue to access the Core as part of the newly established UM-RDCC. The Core also serves investigators in the Schools of Medicine, Dentistry, Pharmacy, Public Health and others in a broad range of basic and medical science disciplines (168 investigators as of December 2000). Members of the UM-MAC (47 users) constitute 49% of the use of the Core, and the UM-MAC provides 24% of the total operating budget of the facility ($258,000 in 2000). In return for this support, UM-MAC members (in the future, UM-RDCC members) are eligible for a 50% discounted recharge rate. Individual investigators deliver pre-processed samples to the Core for flow cytometric analysis of cell sorting. Individual investigators deliver pre-processed samples to the Core for flow cytometric analysis or cell sorting. Scheduling for Core access typically requires a lead-time for 24 hours' notice. The Core is available to investigators from 8:00 AM to 6:00 PM, Monday through Friday, and from 8:00 to 1:00 Saturday. Core instrumentation includes two Beckman-Coulter Elite ESP multi-laser cell sorts, a Becton Dickinson FACS Vantage SE multi-laser high-speed cell sorter, and a Coulter EPICS XL analyzer. Among the broad range of applications available to Flow Cytometry Core users are the following: (a) light scatter measurements assessing cell volume and structural differences; (b) single and multiple intracellular and/or surface immunofluorescence measurements; (c) DNA ploidy measurements and cell cycle analysis; (d) functional measurements of cellular calcium and potassium flux, and oxidative burst; (e) detection and quantitation of apoptotic cell death; (f) cell sorting based on one or more analytical criteria.